You can use a clear coat safe wheel cleaner for aluminum mags. Pinnacle makes one, there are others at an automotive supply store. Works great for tar and other sticky stuff as well.
DAWN works surprising well for a number of cleaning tasks. I use it between my fingers on silver jewelry to remove tarnish! I think there is more than pure soap in it so the rinse thoroughly suggestion is worth following.
All you need is a bottle of Simple Green, it will take it right off and won't hurt the finish. You can also use it to clean your engine, spray it on wait about 5 minutes and rinse. That stuff is amazing. It kept my diesel engines on my past truck so clean, you could eat off them.
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2008 F-250 4X4 Lariat V-10
2002 Airstream Classic 30' w/SO #2074
2007 Kubota 900 RTV
1996 Ford Bronco
2007 Lincoln LT
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